A study on the location of Ureaplasma Urealyticum (UU) in spermatogenic cells in seminal fluid from infertile males was made using rabbit anti-UU antibodies labelled with horse peroxidase (HRP). The results showed that the positive rates of UU in spermatogenic cells were 39.8% (113/284) and 42.2% (35/83)in the infertile males and the males whose wives had history of habitual abortion, respectively. The positive rates of UU were 45.8% (38/83) and 31.6% (30/95)in the patients with positive and negative anti-sperm antibodies, respectively. A high positive rate of UU (73.3%) was found in the infertile males with oligospermia (<20×109/L). The medicines of tetracyclines, such as minomycin, could effectively inhibit the growth of UU, thus converting the UU-positive into negative and improving the patients’fertility. A study on the location of Ureaplasma Urealyticum (UU) in spermatogenic cells in seminal fluid from infertile males was made using rabbit anti-UU antibodies labeled with horse peroxidase (HRP). The results showed that the positive rates of UU in spermatogenic cells were 39.8 % (113/284) and 42.2% (35/83) in the infertile males and the males whose wives had history of habitual abortion, respectively. The positive rates of UU were 45.8% (38/83) and 31.6% (30 / 95) in the patients with positive and negative anti-sperm antibodies, respectively. A high positive rate of UU (73.3%) was found in the infertile males with oligospermia (<20 × 109 / L). The medicines of tetracyclines, such as minomycin, could effectively inhibit the growth of UU, thus converting the UU-positive into negative and improving the patients’fertility.